A general video disk carries a video signal and an audio signal which have been recorded thereon after they have been frequency-modulated (FM) independently of each other. Recently, however, a so-called video disk with digital sound has been developed and commercialized. That is, in this system, an audio signal digitized into a pulse train signal through a predetermined digital modulation system is recorded on the video disk in superposition with FM-modulated video and audio signals. Reference is made to Japanese Patent Unexamined Publication No. 59-171001. By use of such a video disk with digital sound, not only a high quality picture but hi-fi two-channel sound can be obtained.
In an apparatus for reproducing such a video disk with digital sound, generally, the demodulated digital audio outputs for a left channel (hereinafter simply referred to as L-channel) and a right channel (hereinafter simply referred to as R-channel) are respectively for Japanese and foreign language, for example, in the case of a sound multiplex system. As shown in FIG. 7, a digital output demodulated in a PCM decoder 1 is converted into an analog signal by a D/A (digital-to-analog) converter 2, and then applied to sample and hold circuits 3L and 3R provided in the L- and R-channels respectively. In the sample and hold circuits 3L and 3R, the input signals are sampled and held in respective synchronism with L- and R-channel sampling pulses generated from the PCM decoder 1 so as to be separated into analog audio signals for the L-and R-channels. The respective analog audio signals are applied through LPFs (low-pass filters) 4L and 4R and buffer amplifiers 5L and 5R respectively to mode change-over switches 6L and 6R, which are actuated independently of each other. The switches 6L and 6R are switched by L- and R-channel selection signals produced from a selection signal generating circuit 8 so as to select any one of three output modes of the respective audio signals produced at output terminals 7L and 7R of the L- and R-channels. These modes include a first output mode in which Japanese and a foreign language are produced at the output terminals 7L and 7R respectively, a second output mode in which only Japanese is produced at each of the output terminals 7L and 7R, and a third output mode in which only a foreign language is produced at each of the output terminals 7L and 7R. Reference is made to Japanese Patent Unexamined Publication No. 59- 194439.
The conventional apparatus described above is arranged such that the audio signals themselves are switched by the mode change-over switches 6L and 6R, and relays or analog switches are used as those switches 6L and 6R. As a result, there has been such a disadvantage that the sound is deteriorated in quality as well as an S/N ratio as the number of contacts through which the audio signals themselves pass is increased.
Further, in the case where relays are used as the mode change-over switches 6L and 6R, not only two relays but two relay driving circuits are required so that there has been such a disadvantage that not only a large space is required so as to dispose the parts but power consumption is large.